Corrugated cases and cartons have been used in a wide variety of applications such as the packaging of food products and consumer goods, e.g., cereal boxes, precooked and frozen foods. Typically, corrugated cases and cartons are constructed of corrugated or boxboard in which a flat blank is folded and glued to the cooperating parts of the corrugated or carton blank to form a container. Pressure is maintained on the preselected and cooperating parts of the formed carton for a time sufficient for the adhesive to dry or set. Typically, the top and bottom of the erected case or carton also requires to be glued according to the above conditions.
To facilitate the sealing process, thermoplastic and hot melt adhesives have been applied to the cases and cartons by means such as a spray jet, print roller or wheel. In many situations the adhesive is pre-heated by hot air jets to soften and render the adhesive tacky to assist the sealing. Thermosetting adhesives have also been used to facilitate sealing with curing effected by application of heat.
The onsite application of adhesives to the case or carton blank or erected container has created numerous processing issues which often result in run delays and maintenance problems. Hot melt adhesives, which are applied in molten form to the preselected parts of the carton blank, have drawbacks for many reasons. Hot melts, typically are 100 percent solid thermoplastic adhesives, often based on ethylene-vinyl acetate polymers, and need to be heated to between 250–350° F. before being applied to a carton's surface. Because of the high temperatures for application of hot melt adhesives, there are customary health issues resulting from burns and odors. In addition, there are significant issues with respect to the storage, and delivery systems for hot melt adhesives and the maintenance thereof.
Cold set adhesives have been employed in carton formation and sealing but these too present problems. These are slow setting and often incompatible with the high production rate required in the packaging of food products. Water and 100 percent solid based heat sealable polymer systems often do not activate well and many require too high of an activation temperature. Also, the rolled sheets of paperboard stock coated with these adhesives tend to block (stick) together before they can be formed in the carton assembly process and heat sealed.
The following articles and patents are representative of methods for forming cartons:
EP 0017678 A1 discloses the formation of a heat-resistant carton by coating at least one of the carton surfaces with a heat-activated thermosetting adhesive, and then, spraying a water-based adhesive emulsion, e.g., an aqueous emulsion of polyvinyl acetate on the coated surfaces. The carton having the water-based adhesive coated surface is heated by a stream of heated air to at least partially dry the water-based adhesive. The carton surfaces then are placed in contact with each other, and pressure applied for a time sufficient to seal the contacting surfaces together. It is reported that the combination of thermosetting adhesive and water-based adhesive enables the mating surfaces of the carton to be rapidly sealed by automatic carton sealing apparatus.
U.S. Pat. No. 4,490,129 discloses the formation of cartons wherein a water-based adhesive, e.g., polyvinyl acetate is applied in the form of an atomized spray onto selected parts of the carton and then partially dried. Then, the panel to be sealed is pressed together by the punch and die arrangement in carton fabrication.
U.S. Pat. No. 5,228,272 discloses the fabrication of folded paperboard food cartons having a polymer coating on the interior surface and sales graphics on a substantially unplasticized clay coated exterior surface. A water based polymer emulsion such as ethylene/vinyl acetate emulsion is applied by means of a printing press to select areas of the carton blank. Reported in the patent is the use of a full coating of a continuous film of a polymer such as polyethylene, polypropylene and the like to protect against moisture penetration. A water based adhesive (Adcote) is solubilized by acidic modification and adjusted for viscosity by water emulsion is applied by a printing press on select portions and then contacted with a hot air stream and pressed together to fuse the surfaces.
US 2004/0155238 discloses a converting machine comprising a means for depositing a reactivatable adhesive onto a predetermined location of a stock material.